Synthesis, characterisation and catalytic investigation of a new type of PC(sp3)P pincer Pd(ii) complex

Abstract

The diphosphine cis-1,3-bis[(di-tert-butylphosphino)methyl]cyclohexane (2) has been synthesised and its complexation in palladium chemistry has been investigated. Ligand 2 is capable of tricoordination, for instance as demonstrated by an X-ray crystal structure determination of the complex [Pd(2)I], and it is a rare example of a PC(sp³)P pincer ligand. A catalytic study of the Heck reaction revealed that the bis-chelated complex [Pd(2)(CO₂CF₃)] is a highly active, air-stable precatalyst in the olefination of iodo- and bromo-benzenes. It is evident that, in comparison with the analogous aromatic PC(sp²)P system, by switching the hybridisation of the central carbon donor atom from sp² to sp³ improvement in terms of catalytic activity is achieved.